Combustion control method for a direct-injection controlled auto-ignition combustion engine

ABSTRACT

A powertrain and a control method therefore are provided wherein ignition of a combustible charge in a combustion chamber of a controlled auto-ignition internal combustion engine equipped with in-cylinder fuel-injection and a spark ignition device is controlled. A spark-discharge plasma channel is generated between the electrodes of the spark ignition device, and the combustible charge is ignited. The spark-discharge plasma channel is moved toward and entrained by the combustible charge, effective to advance phasing of controlled auto-ignition combustion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/470,037, filed Sep. 5, 2006 now U.S. Pat. No. 7,398,758, which ishereby incorporated by reference in its entirety. The aforementionednon-provisional application claims the benefit of U.S. ProvisionalApplication No. 60/730,186, filed Oct. 25, 2005, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure pertains generally to internal combustion engine controlsystems, and more specifically to a method to control combustion indirect-injection, controlled auto-ignition combustion engines.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

One method of controlling combustion in a conventional internalcombustion engine is with spark-ignition leading to flame propagation,referred to homogeneous-charge spark-ignition (SI). It is well known inconventional homogeneous-charge spark-ignition (SI) engines that cyclicvariability of the ignition process is strongly affected by in-cylindercharge motion during spark discharge. For example, it has beendemonstrated that better ignition characteristics resulted by convectingan early flame-kernel away from each spark electrode to minimize sparkenergy loss. In particular, in-cylinder charge motion, e.g., swirl andtumble components, in conjunction with combustion chamber design havebeen used to manipulate a spark-discharge plasma channel away from thespark-plug electrodes. This action improves ignitability of bothstoichiometric and dilute air/fuel mixtures in both homogeneous-chargeand stratified-charge spark-ignition gasoline engines.

The importance of using spark-ignition for combustion phasing control indirect-injection controlled auto-ignition combustion engines has alsobeen demonstrated. Use of spark-ignition to control combustion phasingin a direct-injection gasoline auto-ignition combustion engine operatingat light load and idle, and to enable cold start using a conventionalcompression ratio has been described in U.S. Pat. No. 6,971,365 B1,entitled AUTO-IGNITION GASOLINE ENGINE COMBUSTION CHAMBER AND METHOD,issued to Najt, et al., on Dec. 6, 2005. Use of fuel injection andspark-ignition strategies to extend the mid-load operation limit of agasoline direct-injection controlled auto-ignition combustion engine hasbeen described in U.S. Pat. No. 6,994,072 B2, entitled METHOD FOR MIDLOAD OPERATION OF AUTO-IGNITION COMBUSTION, issued to Kuo, et al., onFeb. 7, 2006. There are many geometrically constrained designlimitations for optimal engine operation which affect the ability of thespark-discharge plasma channel to be located at an ignitable region ofthe fuel-air mixture; these included relative position between the sparkplug, the fuel injector, combustion-chamber geometry, and piston-bowlgeometry.

There is a need for a powertrain control system, comprising either ahomogeneous- or stratified-charge, controlled auto-ignition internalcombustion engine, wherein ignition of a combustible charge in acombustion chamber is controlled.

SUMMARY

A powertrain includes an internal combustion engine having a combustionchamber with an in-cylinder fuel injector and a spark-ignition device.The engine is operative in a controlled auto-ignition combustion mode.The powertrain further includes a control module configured to execute acomputer program to generate a combustible charge and control ignitionthereof. The computer program includes code to control the sparkignition device to generate a spark-discharge plasma channel betweencathode and anode electrodes of the spark ignition device, and code toactuate the in-cylinder fuel injector to generate the combustible chargein the combustion chamber effective to move the spark-discharge plasmachannel toward the combustible charge to advance phasing ofauto-ignition of the combustible charge.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIGS. 1, 2, and 3A-3D are schematic illustrations of an internalcombustion engine, in accordance with the present disclosure; and,

FIGS. 4, 5, and 6 are datagraphs, in accordance with the presentdisclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the depictions are for thepurpose of illustrating certain exemplary embodiments only and not forthe purpose of limiting the same, FIG. 1 depicts a powertrain,comprising an internal combustion engine 10 and control system 5 whichhas been constructed in accordance with one embodiment. The engine 10preferably comprises a gasoline direct-fuel injection, spark-ignited,four-stroke internal combustion engine operable in a controlledauto-ignition process, i.e., a homogeneous-charge, compression-ignition(‘HCCI’) engine. It is understood that the descriptions herein areapplicable to other engine configurations, e.g., engines configured tooperate in a stratified-charge mode.

The exemplary engine comprises a plurality of variable volume combustionchambers 20, each defined by a closed-end cylinder formed in an engineblock 25. A moveable piston 11 defines, with walls of the cylinder, thevariable volume combustion chamber 20. A rotatable crankshaft 35 isconnected by a connecting rod to each piston 11, which reciprocates inthe cylinder during ongoing operation. A cylinder head 27 is sealablyattached to the block 25 at an end thereof distal from the crankshaft35, and forms the combustion chamber 20 with the cylinder walls and thepiston 11. The cylinder head 27 provides a structure for intake port 17,exhaust port 19, intake valve(s) 21, exhaust valve(s) 23, in-cylinderfuel injector 12, and spark plug 14. The fuel injector 12 comprises aknown device which is fluidly connected to a pressurized fuel supplysystem to receive fuel, is operative to directly inject or spray thepressurized fuel into the combustion chamber 20 periodically duringongoing operation of the engine. Actuation of the fuel injector 12, andother actuators described herein, is controlled by an electronic enginecontrol module (‘ECM’), which is an element of the control system 5.Spark plug 14 comprises a known device operative to ignite an air/fuelmixture formed in the combustion chamber 20. The spark plug includes ananode electrode 15 and a cathode electrode 16, wherein a spark plug gapis formed therebetween. Requisite ignition energy is delivered to thecathode electrode 16 of the spark plug 14 for discharge across the sparkplug gap, at appropriate times, from an ignition module controlled bythe ECM. The intake port 17 channels air to the combustion chamber. Flowof air into the combustion chamber 20 is controlled by one or moreintake valves 21, operatively controlled by a valve actuation devicesuch as a camshaft (not shown). Combusted (burned) gases flow from thecombustion chamber 20 via the exhaust port 19, with the flow ofcombusted gases through the exhaust port controlled by one or moreexhaust valves 23 operatively controlled by a valve actuation devicesuch as a second camshaft (not shown). Specific details of a controlscheme to control opening and closing of the valves are not detailed,but it is understood that various valve control mechanisms and schemes,such as variable cam phasing and variable valve actuation, fall withinthe purview of the disclosure. Other generally known aspects of engineand combustion control are not detailed herein.

As previously described, the ECM is preferably an element of the overallcontrol system 5 comprising a distributed control module architectureoperative to provide coordinated powertrain system control. The ECMsynthesizes pertinent information and inputs from sensing devices,including a crank sensor 31 and an exhaust gas sensor 40, and executesalgorithms to control operation of various actuators, e.g. the fuelinjector 12 and the ignition module, to achieve control targets,including such parameters as fuel economy, emissions, performance,driveability, and protection of hardware. The ECM is preferably ageneral-purpose digital computer generally comprising a microprocessoror central processing unit, storage mediums comprising read only memory(ROM), random access memory (RAM), electrically programmable read onlymemory (EPROM), high speed clock, analog-to-digital (A/D) anddigital-to-analog (D/A) circuitry, and input/output circuitry anddevices (I/O) and appropriate signal conditioning and buffer circuitry.A set of control algorithms, comprising resident program instructionsand calibrations, is stored in ROM and executed to provide therespective functions. Algorithms are typically executed during presetloop cycles such that each algorithm is executed at least once each loopcycle. Algorithms stored in the non-volatile memory devices are executedby the central processing unit and are operable to monitor inputs fromthe sensing devices and execute control and diagnostic routines tocontrol operation of the respective device, using preset calibrations.Loop cycles are typically executed at regular intervals, for exampleeach 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engineand vehicle operation. Alternatively, algorithms may be executed inresponse to occurrence of an event.

Referring now to FIGS. 2 and 3A-3D, a method for controlling ignition ofa combustible charge 60 in the combustion chamber 20 of theaforementioned engine 10 is illustrated. The method, preferablyincluding at least one algorithm executed in the ECM, comprisesgenerating a spark-discharge plasma channel 50 between the electrodes ofthe spark ignition device, and generating the combustible charge 60 inthe combustion chamber 20 through actuation of the fuel injector 12. Thespark-discharge plasma channel 50 formed between the cathode electrode16 and anode electrode 15 comprises a high-temperature ionized gascolumn. The spark-discharge plasma channel is moved and entrained in thecombustible charge effective to advance phasing of controlledauto-ignition of the combustible charge, relative to rotation of thecrank angle. The combustible charge 60 comprises a mixture of air, fueland residual gases captured in the combustion chamber during acompression phase of the four-stroke engine. Generating the combustiblecharge in the combustion chamber comprises selectively controlling fuelinjection timing relative to piston position to generatefuel-spray-induced charge motion in the combustion chamber to entrainthe spark-discharge plasma channel, including controlling timing andtargeting of the in-cylinder fuel injection. It further comprisescontrolling magnitude and timing of openings of intake and exhaustvalves to the combustion chamber to control in-cylinder charge motion.

The in-cylinder charge motion is defined herein as velocity and momentumof in-cylinder gases comprising the in-cylinder charge. Constituents ofthe in-cylinder charge include fresh intake air ingested during anintake stroke, any residual-gas fraction, and, directly injected fuel.The residual gas is defined as gas trapped from a previous engine cycle,or gas ingested from the exhaust during the intake stroke due to valveoverlap or external exhaust gas recirculation. The velocity and momentumof the in-cylinder charge motion is preferably controllable withreference to flow-control parameters, including: the fresh intake airingested through the intake valves, the residual gas flow, the injectedfuel, and the shape and design of the combustion-chamber shape includingthe piston top, as well as interaction of these parameters during intakeand compression strokes.

The velocity and momentum of the in-cylinder charge motion, and theassociated flow control parameters are affected various combustionchamber design and operating factors. These factors comprise geometricdesign and shape of the combustion chamber and any bowl at the top ofeach piston, placement of the fuel injector in the combustion chamber;quantity and location of intake and exhaust valves, location of thespark plug; and, timing and magnitude of openings and closings of theintake and exhaust valves. Combustion phasing is defined herein as thetiming, in crank-angle degrees, at which 50 percent of the mass of thecombustible charge is burned (‘ca50’), typically after top-dead-center(‘aTDC’).

Referring now to FIGS. 3A-3D, further details are shown of the fuelinjection system of FIG. 2, shown as four sketches which depict imagescaptured within an exemplary cylinder constructed in accordance with theengine described with reference to FIG. 1. The images were capturedusing photographic equipment and techniques operative to visually recordin-cylinder events during a single engine cycle. Locations of the sparkplug cathode electrode and anode electrode have been enhanced and anX-scale has been added to facilitate linear measurement for morecomplete understanding. The X-scale includes a zero point concurrent acenterline formed by the spark plug cathode electrode 16, in order todemonstrate activity of interest within the combustion chamber 20.Movement and entrainment of the spark-discharge plasma channel byin-cylinder charge motion using direct fuel injection was recorded, andmeasured as a linear excursion along the X-axis away from the spark plugcathode electrode 16. In FIG. 3A, the spark plasma channel 50 begins onthe left side of the center of the cathode electrode 16 and designatedas a negative direction. In FIG. 3B, fuel injected during an injectorspray event becomes visible, depicted as combustible charge 60, andbegins to move the spark plasma channel 50 toward a positiveX-direction. Movement and thus entrainment of the spark channelcontinues through FIG. 3C and the spark plasma channel 50 is seen to bedrawn completely out of the spark plug gap by the end of the injectionevent, as depicted in FIG. 3D. The injected fuel disappears in FIG. 3Ddue to vaporization, leaving a fuel-air mixture into which the sparkplasma channel 50 has been drawn.

Referring now to FIGS. 4 and 5, two graphs are shown depicting theeffect of spark-channel entrainment (illustrated in FIG. 3), caused bycylinder-charge motion using direct fuel-injection on controlledauto-ignition combustion phasing. The graph shown in FIG. 4 depicts thecrank angle at fifty percent mass burned (ca50), measured in terms ofdegrees after top-dead-center (deg aTDC), as a function of maximumplasma excursion from the center of the electrode, in millimeters.Auto-ignition combustion phasing is defined as the crank angle at which50 percent of the mass has burned (ca50). The data depicted as “x” arethose cycles that experienced little entrainment by the spray and thusthe maximum excursion, Xmax, was less than +2 mm from the center of theelectrodes. The data depicted as “•” are those cycles with entrainmentfor which the maximum excursion, Xmax, was greater than +2 mm from thecenter of the electrodes. FIG. 5 comprises a graph showing the number ofcycles achieving each crank angle at which fifty percent mass is burned(ca50) from the two cases delineated in FIG. 4; namely, the poorlyentrained cycles (Xmax<2 mm) and highly entrained cycles (Xmax>2 mm). Inparticular, cycles with plasma-channel entrainment less than +2 mm had alow probability of advanced phasing. Plasma channels with Xmax>+2 mm hada high probability of advancing the auto-ignition combustion phasing tocrank angle at which fifty percent mass is burned (ca50) prior to 5 degaTDC. FIGS. 4 and 5 indicate that plasma-channel entrainment by fuelspray is a necessary but not sufficient condition for advancedauto-ignition combustion phasing.

Referring now to FIG. 6, a graph depicting frequency of occurrence ofmaximum excursions from center of the electrode for a fired cylinder(i.e., fuel injected) and a motored cylinder (i.e., no fuel injection),is shown for 500 engine cycles. The results shown in FIG. 6 demonstratethat in-cylinder charge motion created by direct fuel injectionincreases the probability that the spark-discharge plasma channel 50 ismoved and entrained in the positive X-direction. In particular, themaximum value of the plasma-channel excursion (in the X-direction)during each spark discharge has been computed from photographic imagesfor the 500 engine cycles. The results depicted as the dashed line inFIG. 6 demonstrate that, in the motored engine with no fuel injection,the spark plasma channel 50 has a nearly equal probability to be movedin both the positive and the negative directions. This result occurs dueto the in-cylinder charge motion generated by various flow-controlparameters, including fresh intake air ingested through the intake port17, residual gas flow, shape of the combustion-chamber 20, including thecylinder head 27 and top of the piston 11, and interaction of theseflow-control parameters during intake and compression strokes. The flowcontrol parameters and the direct injection of the fuel operate tocontrol velocity and momentum of the in-cylinder charge motion. Incontrast, the results depicted in FIG. 6 as a solid line demonstratethat during engine operation with direct fuel injection andauto-ignition combustion, the plasma channel is preferentially entrainedby the fuel injection spray toward the positive X-direction.

In summary, the viability of the present embodiment is clearlydemonstrated wherein, by optimizing both fuel injection timing andtargeting, the spark-discharge plasma channel was entrained by thein-cylinder charge motion induced primarily by the fuel spray. Theefficacy of the present embodiment was demonstrated in FIGS. 4-6 whereinit is demonstrated that the in-cylinder charge motion created by thedirect fuel injection advanced the combustion phasing in a controlledauto-ignition combustion engine.

The present disclosure presents a method to manipulate thespark-discharge plasma channel with the in-cylinder flow for combustioncontrol in the direct-injection controlled auto-ignition combustionengine. In particular, it offers method to control the auto-ignitioncombustion phasing. The combustion phasing is defined here as the timingin crank-angle degrees at which 50 percent of the mass is burned (ca50).Potential benefits of the present disclosure include: 1) improvedindividual cylinder combustion control during speed and load transientsin a multi-cylinder engine and 2) relaxed the geometric constraintssomewhat for better combustion system design. The present disclosureapplies to controlled auto-ignition combustion engines operated with anysingle- or multi-component fuel. Benefits of the present disclosureinclude an improved individual cylinder combustion control during speedand load transient conditions, and more robust combustion system designrelated to geometric constraints.

The disclosure has described certain preferred embodiments andmodifications thereto. This can include various engine configurationsincluding a free-piston linear alternator, or a two-strokecrank-and-slider engine. Further modifications and alterations may occurto others upon reading and understanding the specification. Therefore,it is intended that the disclosure not be limited to the particularembodiment(s) disclosed as the best mode contemplated for carrying outthis disclosure, but that the disclosure will include all embodimentsfalling within the scope of the appended claims.

1. Powertrain, comprising: an internal combustion engine, including acombustion chamber having an in-cylinder fuel injector and aspark-ignition device, said engine operative in a controlledauto-ignition combustion mode; and a control module configured tocontrol the spark ignition device to generate a spark-discharge plasmachannel between cathode and anode electrodes of the spark ignitiondevice, and actuate the in-cylinder fuel injector to generate acombustible charge in the combustion chamber and generatefuel-spray-induced motion in the combustion chamber to draw thespark-discharge plasma channel toward the combustible charge to advancephasing of auto-ignition of the combustible charge.
 2. The powertrain ofclaim 1, wherein the control module is configured to adjust one ofmagnitude and timing of openings of intake and exhaust valves of thecombustion chamber to generate the fuel-spray-induced motion in thecombustion chamber.
 3. The powertrain of claim 1, further comprising thecombustion chamber and the piston top designed to generate charge motionof the combustible charge in the combustion chamber to entrain thespark-discharge plasma channel, and the control module configured toactuate the in-cylinder fuel injector to generate the fuel-spray-inducedmotion in the combustion chamber to draw the entrained spark-dischargeplasma channel toward the combustible charge to advance the phasing ofauto-ignition of the combustible charge.
 4. The powertrain of claim 1,wherein the control module configured to actuate the in-cylinder fuelinjector to generate the combustible charge in the combustion chamberfurther comprises the control module configured to control timing toactuate the in-cylinder fuel injector.
 5. The powertrain of claim 1,wherein the in-cylinder fuel injector is targeted to generate thecombustible charge in the combustion chamber to move the spark-dischargeplasma channel in the combustible charge to advance phasing of thecontrolled auto-ignition combustion.
 6. The powertrain of claim 1,further comprising the control module configured to selectively actuatethe in-cylinder fuel injector to generate the combustible charge in thecombustion chamber and generate fuel-spray-induced motion in thecombustion chamber to draw a portion of the spark-discharge plasmachannel toward the combustible charge a lateral distance of at least twomillimeters from a centerline formed by the cathode electrode of thespark ignition device.
 7. The powertrain of claim 1, wherein thecontrolled auto-ignition internal combustion engine comprises ahomogeneous-charge, compression-ignition engine.
 8. The powertrain ofclaim 1, wherein the controlled auto-ignition internal combustion enginecomprises a stratified-charge engine.
 9. Method to control combustion ina homogeneous-charge, direct-injection, controlled auto-ignitioninternal combustion engine, comprising: creating a spark-dischargeplasma channel between electrodes of a spark plug; and controlling thespark-discharge plasma channel by controlling an in-cylinder combustioncharge, including controlling timing and targeting of fuel injectionfrom an in-cylinder fuel injector to generate the combustion charge inthe combustion chamber and generating fuel-spray-induced motion in thecombustion chamber to draw the spark-discharge plasma channel toward thecombustion charge to advance phasing of auto-ignition of the combustioncharge.